Today, off-highway trucks with carrying capacities from as low as twenty five (25) to four hundred (400) tons or more are used in a number of off road environments for hauling a variety of materials. As the “off-highway” name implies, use of these trucks is limited to off-highway, private roads such as in quarries, landfills, mines, steel mills, power plants. As such the typical norm is for these off-highway trucks to operate on unpaved gravel/aggregate roads (“haul roads”). One of the significant challenges of operating off-highway trucks on these private gravel/aggregate roads is the dust that can be created as the trucks travel back and forth between destinations. The dust created as the off-highway trucks travel on these unpaved roads causes both an environmental problem and a safety (visibility) problem.
This off-highway road dust necessitates spreading dust suppressant on the off-highway truck haul roads. This dust suppressant normally takes the form of water sprayed on the haul roads by large water truck tankers. Although the haul road water suppresses the dust, it unfortunately at the same time often causes the haul roads to become muddy. One large Western United States mine reports that on hot summer days they have to spread almost three million (3,000,0000) gallons of dust suppressant water a day on their off-highway truck haul roads. When spreading this much water, it is inevitable that some areas on the haul roads are overwatered and, accordingly, exceptionally muddy for some period of time until the water is absorbed into the ground or evaporates.
Mines often have off-highway truck fleets of as many as fifty (50) to one hundred (100) off-highway trucks. A typical off-highway truck fleet might consist of two hundred fifty (250) ton capacity off-highway trucks, each of which cost upwards of $2,750,000.00 USD to $3,500,000.00 USD. Accordingly, a mine's capital investment in off-highway truck fleets and the ancillary equipment needed to support such a fleet typically necessitates operating such fleets twenty four (24) hours a day, three hundred sixty (360) plus days a year. And, when operating around the clock, a mines environmental conditions are often challenging—e.g., rain, snow, sleet and the like—which also impacts haul road conditions, creating poor haul road conditions that include slippery, muddy haul roads.
Muddy, poor haul road conditions result in mud being thrown up by the off-highway truck's tires. This mud invariably sticks to the off-highway truck chassis/body underside. One can appreciate that on some days it is first dust collecting on the underside of an off-highway truck chassis/body, then wet sticky mud, then more dust, etc., through an endlessly repeated cycle. And as this road ‘debris’ is thrown up onto the underside of the body by the off-highway truck tires, the movement of the off-highway truck causes air flow that dries the mud enough so even more mud sticks to what is already stuck to the off-highway truck body. This layering or build up process is something like making adobe bricks, resulting in a thick layer of caked-on, mud.
In freezing environs this build up of mud is even worse. As wet road ‘debris’ is thrown up from the tires it further sticks to the underside of an off-highway truck chassis/body both by the natural cohesiveness of the road ‘debris’ and the stickiness resulting from the freezing nature of this ‘debris’ when it mixes with snow fall, rain, etc. No matter the time of the year or environmental conditions, road ‘debris’ that collects on a haulage vehicle is detrimental to the hauling capabilities of a truck.
The payload hauling capacity of an off-highway truck is determined as follows:Maximum Gross Vehicle Weight−Net Vehicle Weight (i.e., empty vehicle weight)=Full Payload,  (1)where Maximum Gross Vehicle Weight is the weight that an off-highway truck is rated to safely carry, which is typically limited by tire capacity. However, any ‘debris’ that is carried on the outside of an off-highway truck body or truck chassis, as thrown up by the truck tires, etc. also needs to be factored into the “Net Vehicle Weight.”
One prominent off-highway truck manufacturer has established a four (4) percent of ‘clean’ Net Vehicle Weight ‘debris’ benchmark allowance, and increases Net Vehicle Weight by this factor to arrive at a “Factored Net Vehicle Weight” in the above formula—i.e., 1.04 times Net Vehicle Weight=Factored Net Vehicle Weight.
Typical 250 ton capacity off-highway trucks have a ‘clean’ Net Vehicle Weight of 250,000 pounds so the ‘debris’ allowance would be (250,000×0.04=10,000 pounds) or five (5) tons of Lost Payload capabilities. Likewise a 400 ton capacity off-highway truck having a ‘clean’ Net Vehicle Weight of 475,000 pounds would have a ‘debris’ allowance or payload reduction of 19,000 pounds or nine and one half (9.5) tons Lost Payload.
Replacing the “Net Vehicle Weight” in the Full Payload equation (1) above with the updated “Factored Net Vehicle Weight” gives a “Factored” or “Achievable” Payload.Maximum Gross Vehicle Weight−“Factored Net Vehicle Weight” (i.e., empty vehicle weight)=Factored or Achievable Payload,  (2)which is 98% of the Full Payload, assuming the 4% example referenced above for the amount of debris carried on the vehicle. As suggested by the examples given above, the 4% debris factor is a significant amount of material for these large capacity trucks and when summed over many haul cycles reflects a significant reduction in the hauling efficiency of the trucks.
On a large off-highway truck with a “rated” payload of four hundred (400) tons the actual “effective” payload could really be nine and a half (9.5) tons of outside ‘debris’ and possibly, if off-highway truck body inside material carryback is also occurring an additional twelve (12) tons of body inside ‘carryback’ could exist for a total of twenty one and one half (21.5) tons of outside body ‘debris’ and inside body material carryback. Thus, the off-highway truck which was purchased as a four hundred (400) ton off-highway truck is in reality about a three hundred eighty (380) ton or less truck. That's a four (4) percent loss in carrying capacity. If an off-highway truck costs $12,000.00 to $16,000,00 USD per ton of hauling capacity, this nine and one half (9.5) tons of ‘debris’ converts to a $240,000.00 to $320,000.00 payload carrying loss per truck.
Thus, the elimination of truck ‘debris’ and truck ‘carryback’ is economically very important and very cost effective as well as being operationally safety driven.
Payload capacity for on-highway trucks is similarly compromised by debris. Payload carrying capacity of on-highway trucks is more typically set by State Gross Vehicle Weight Regulations. Various State Departments of Transportation on a state-by-state basis establish maximum road Gross Vehicle Weights. These maximum Gross Vehicle Weights vary from road type to road type; Interstate Roads, Primary State Roads, Secondary Roads, etc. And further in some states at various times of the year there are “frost laws” that reduce the maximum value of the Gross Vehicle Weight.
On-highway trucks often have the carrying capacity to haul significantly more Gross Vehicle Weight than is typically allowed by most state's Departments of Transportation. Accordingly, if a particular on-highway truck load is indivisible, then special permits are typically available to permit the movement of such loads with higher Gross Vehicle Weights. But such permits are typically only issued when the load is indivisible. In all other situations, any debris on/in an on-highway truck immediately and directly adds to the on-highway trucks Gross Vehicle Weight and subtracts from the maximum allowable payload capacity of the truck.
Just like debris retained on off-road trucks, debris retained on on-highway trucks, results in reduce payload capacity and Lost Payload.